1. Field of the Invention
The present invention relates to a carriage used for a storage-retrieval system.
2. Description of the Related Art
A typical storage-retrieval system includes a shelf assembly having a plurality of shelves disposed at various heights, and a carriage movable along the front surface of the shelf assembly. In such a storage-retrieval system, the carriage is automatically lead to a desired storage portion of the shelf assembly. Then, the shifting operation of an object such as a cargo for example is performed from the shelf assembly onto the carriage or vice versa.
The above carriage includes a pair of movable devices arranged to reciprocate toward and away from the shelf assembly. Each movable device is provided with engaging members arranged to selectively assume a closed position and an open position. In closed position the engaging members are brought into contact with the object to be shifted, while in the open position the engaging members are brought out of contact with the object. During the shifting operation, the movable devices are actuated, with the engaging members held in the closed position. As a result, the object is shifted between the carriage and the storage portion of the shelf assembly.
There are various kinds of movable devices having the above arrangement. One example is disclosed in Japanese Patent Application Laid-open No. 7-101508. The carriage disclosed in this document is schematically shown in FIG. 95 of the accompanying drawings. Specifically, the carriage includes an illustrated base member which supports a pair of shifting members 170 capable of moving toward and away from a shelf assembly (not shown). Both ends of each shifting member 170 are provided with engaging members 171. The illustrated engaging member is arranged to pivot around a horizontal shaft between an upright position and an inwardly horizontal position. The pivotal movement of the engaging member 171 is driven by an unillustrated motor via a chain 173. The chain 173 engages two sprockets 174.
The above prior art carriage has the following problems. Specifically, when an object to be shifted is not placed at a proper position in a storage region 175 or on the carriage, the object may obstruct the pivotal movement of the engaging member 171. In such a case, the engaging member 171 is unable to assume the closed position (the horizontal position), resulting in failure to perform the intended shifting of the object W. Further, with the prior art arrangement, the moment acting on engaging members 171 during the shifting operation of the object W will be concentrated at a fixing portion of the engaging member 171 to the shifting member 170. Thus, the engaging member 171 and the shifting member 170 will be damaged at a relatively earlier stage.
Further, the width E of the shifting member 170 needs to be as small as possible so that the carriage handles a larger object W. However, when the width E of the shifting member is reduced, the width of the engaging member 171 should be reduced accordingly. In this case, the area of the engaging member 171 to contact the object W is so small that unfavorable damage or deformation will be caused on the object W. This problem will become more serious when the object W is a cardboard box for example.
Still further, it is difficult or even impossible for the prior art carriage to handle a rather tall object W due to the chain 173 provided between the upper surfaces of the respective shifting members 170.